Add alternate comparison types to versions

- The types are:
-- Previous: The default and the previously used type
-- Subsequent: Compares against the next version
-- Current: Compares against the current version
- Allow switching between comparison types in index and diff views
-- Have links vary depending upon current comparison type

app/controllers/application_controller.rb

@@ -39,6 +39,10 @@ class ApplicationController < ActionController::Base
     super
   end
 
+  def set_version_comparison
+    params[:type] = %w[previous subsequent current].include?(params[:type]) ? params[:type] : "previous"
+  end
+
   def model_name
     controller_name.classify
   end

app/controllers/artist_commentary_versions_controller.rb

@@ -2,6 +2,7 @@ class ArtistCommentaryVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @commentary_versions = ArtistCommentaryVersion.paginated_search(params)
     @commentary_versions = @commentary_versions.includes(:updater, post: :uploader) if request.format.html?
 

app/controllers/artist_versions_controller.rb

@@ -2,6 +2,7 @@ class ArtistVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @artist_versions = ArtistVersion.paginated_search(params)
     @artist_versions = @artist_versions.includes(:updater, artist: :urls) if request.format.html?
 

app/controllers/note_versions_controller.rb

@@ -2,6 +2,7 @@ class NoteVersionsController < ApplicationController
   respond_to :html, :xml, :json
 
   def index
+    set_version_comparison
     @note_versions = NoteVersion.paginated_search(params)
     @note_versions = @note_versions.includes(:updater) if request.format.html?
 

app/controllers/pool_versions_controller.rb

@@ -4,6 +4,7 @@ class PoolVersionsController < ApplicationController
   around_action :set_timeout
 
   def index
+    set_version_comparison
     @pool_versions = PoolVersion.paginated_search(params)
     @pool_versions = @pool_versions.includes(:updater, :pool) if request.format.html?
 
@@ -19,7 +20,8 @@ class PoolVersionsController < ApplicationController
     if params[:other_id]
       @other_version = PoolVersion.find(params[:other_id])
     else
-      @other_version = @pool_version.previous
+      set_version_comparison
+      @other_version = @pool_version.send(params[:type])
     end
   end
 

app/controllers/post_versions_controller.rb

@@ -6,6 +6,7 @@ class PostVersionsController < ApplicationController
   respond_to :js, only: [:undo]
 
   def index
+    set_version_comparison
     @post_versions = PostVersion.paginated_search(params)
 
     if request.format.html?

app/controllers/wiki_page_versions_controller.rb

@@ -3,6 +3,7 @@ class WikiPageVersionsController < ApplicationController
   layout "sidebar"
 
   def index
+    set_version_comparison
     @wiki_page_versions = WikiPageVersion.paginated_search(params)
     @wiki_page_versions = @wiki_page_versions.includes(:updater) if request.format.html?
 
@@ -16,15 +17,20 @@ class WikiPageVersionsController < ApplicationController
 
   def diff
     if params[:thispage].blank? || params[:otherpage].blank?
-      redirect_back fallback_location: wiki_pages_path, notice: "You must select two versions to diff"
-      return
-    end
-
-    @thispage = WikiPageVersion.find(params[:thispage])
-    @otherpage = WikiPageVersion.find(params[:otherpage])
-
-    if @thispage.id < @otherpage.id
-      @thispage, @otherpage = @otherpage, @thispage
+      page_id = params[:thispage] || params[:otherpage]
+      if page_id.blank?
+        redirect_back fallback_location: wiki_pages_path, notice: "You must select at least one version to diff"
+        return
+      end
+      set_version_comparison
+      @thispage = WikiPageVersion.find(page_id)
+      @otherpage = @thispage.send(params[:type])
+    else
+      @thispage = WikiPageVersion.find(params[:thispage])
+      @otherpage = WikiPageVersion.find(params[:otherpage])
+      if @thispage.id < @otherpage.id
+        @thispage, @otherpage = @otherpage, @thispage
+      end
     end
 
     respond_with([@thispage, @otherpage])